Oscillation generator



Jan. 6, 1931. P. THoMAs 1,788,131 oscILLATIoN GENERATOR Filed July 15, 1927 TINILHh-ITAIIMHHILIIIIH- .5'4 L 6 IIH 'NIH

INVENTOR 'ATTORNEY Patented Jan. 6,1931 i PHILLIPS THOMAS, or EDGEWooD, PENNSYLvnNrm-ssrdnoa *ro wizsINGoua -'ELEcrnIc a MANUFAcrUnrNG COMPANY, A conroRATIoN or rENNsYLvANrA J oscILLA'rIoN GENERATOR Application lei July 15, 1927. Serial No. 205,924.,

My invention relatesv to oscillation generators, and it has particular lrelation to generators of the thermionic-tube type designed to handle ultra-high frequencies.

lThe production and radiation of any considerablerv amount of power at ultra-high frequencies has heretofore been attended by numerous difiiculties. The peculiarities of the variouscircuits used in connection with the generation of oscillations at the usual frequencies employed in radio transmission are greatly emphasized when such circuits are given the reduced dimensions necessary for ultra-high frequencies, and, consequently, unless many precautions are taken, the amount of power radiated may be vastly less than the predicted amount.

It has also been found extremely difficult to devise an ultra-high frequency oscillation generator that is stable in operation. Numerous factors, such as varying electron emission from the tube filament, the influence of various stray capacities, physical changesin the circuit elements, etc., have all .contributed toward causing the oscillation-frequency to vary from instant to instant, and have heretofore very seriously interfered with the production of oscillations at wave-lengths of the order of fractions of a meter.

It is, accordingly, an object of my invention to provide an ultra-high-frequency oscillation generator that is stable 1n operation. v

Another object of my invention is to provide an ultra-high-frequency oscillation generator that is capable of a much higher power output than the generators known to the prior art.

Another object of my invention is to provide an ultra-high-frequency oscillation generator that is capable of radiating energy directly, without the necessity of employing a specific radiatingl structure analogous to a loop or antenna.

Another object of my invention is to provide, in a generating system of the type Vdescribed means for 1solating portions thereof subject to high frequencies from other portions thereof -without introducing losses.

In order to accomplish the above objects,.I A

have found it advisable to utilize a specially desi ed thermionic tube in which the connectlon to the plate extends through .the glass envelope at a point opposite to the polnts through which the grid and filament entend. In addition, I eliminate the necessity for employing radio-frequency chokecoils in certain of the power supplyleads,

by substituting therefor plain conductors having a length which is a definite fraction of the wave length of the-frequency of the oscillations generated.

I provide also a stabilizing oscillatory-circuit having a natural period comparable to thefrequency of the oscillations generated. The stabilizing circuit enables me to generate oscillations at wave lengths much shorter than those heretofore employed, and to obtain power outputs much greater than those obtainable with circuits known to the prior art.

Among the novel features of my/invention, are those particularly set forth in the appended claims. The invention itself, however, both as to its organization and its method of operation, togetherwith further objects and advantages thereof, will best be understood from a consideration of the following description of certain specific emcords 5 and 6, or other insulating devices,-

from a horizontally extending supporting bar 7 which, in turn, is carried by a stand 8.

-The plate 2 is provided with input conductors 10 which extend through one end of the glass envelope. The filament 8 is pro I tor 36.

vided with two conductors 11 and 12- which extend through the end of the glass envelope at a point opposite to the point at which the plate conductor 10 extends therethrough. The grid comprises a helical conductor 13 wound on two supporting members 14 and 15 which, in turn, are carried by a plurality of lead-in conductors 16 and 17 which extend to the outside of the glass envelope and are there joined together.

An oscillatory circuit 18, com )rising a single loop 20 of copper tubing an a fixed condenser 21 constituted by plates 22 and 23 soldered to the ends of the tubing, its connected to the plate of the thermionic device through a stopping condenser 24 and to the grid of the device through a conductor 25.

The filament is supplied with energy from a source 26 through leads 27 and 28 which are one-quarter wave length long, the points at which these leads are connected to the source 26 being grounded through condensers 30 and 31. The positive pole of a C-battery 32 is connected to the midpoint of the filament-voltage source 26, and the negative pole thereof is preferably connected, by a conductor 33, to the physical center of the oscillatory circuit 18.

A source 34 of direct current is provided, the negative pole of which is connected to the midpoint of the filament-supply battery 26 by means of a conductor 35, and the positive pole of which is connected to the plate of the thermionic device by means of a conduc- The conductor 36 is connected to ground through a condenser 37, the length of the conductor 36 between the condenser and the plate lead-in conductor 10 being onequarter of a wave length of the oscillations to be generated.

The negative pole of the direct-current source 34 is grounded through a condenser 38, and the negative pole of the C-battery is grounded through a condenser 39.

The frequency generated by a system arranged according to Fig. 1, depends principally vupon the capacity between the plate and the grid of`the thermionic device, upon the length of the electrode supports in the interior of the tube, and also upon the length of an exterior connection between the grid and anode, which connection is necessary in order to include the blocking condenser 24 if the auxiliary stabilizing circuit 18 is not present. A circuit of this general character is shown in Fig. 2, in which ligure the blocking condenser 2-1 referred to is represented by dotted lines.

When the stabilizing circuit, including the single-turn inductor 20 and the fixed condenser 21, is coupled to the thermionic device, as shown, it is necessary that the fixed condenser shall have a capacity of the same order of magnitude as the grid-plate capacity of the tube. The single-turn inductor, therefore, must possess an induetance practically equal to the distributed induetance of the lead-in conductors associated with the tube and the induetance of the conductors necessary to associate the. blocking condenser therewith.

The system, as shown, therefore, comprises two coupled oscillatory circuits having substantiall the same natural period. The thermionic evice, by reason of its physical dimensions, tends to oscillate at a definite frequency, and the stabilizing circuit also tends to oscillate at this same frequency. As a consequence, the generation of oscillations is greatly stabilized by the presence of the auxiliary circuit, which circuit in no way militates against the reneration of oscillations at as high frequencies as the characteristics of the thermionic device will permit.

` The potential of the midpoint of the stabil-l izing circuit is fixed by its connection to ground through the condenser 39, which is preferably of large capacity. This point is, therefore, a voltage node or a point which is maintained at substantially zero voltage, insofar as radio-frequency oscillations are concerned. The plates 22 and 23, constituting the fixed condenser in the auxiliary circuit 18Z are analogous to voltage loops. The

terms voltage nodes and voltage loops, while not strictly correct, insofar as conditions in my improved oscillation generating system are concerned, are believed snflieiently accurate to characterize those points therein which are subject to but little highfrequency-potential variation and those subject to maximum high-frequency-potential variation, respectively.

ln one actual embodiment of my invention, the. leads 36, 27 and 28 were 50 centimeters long and the over-all length of the tube itself was 17.78 centimeters, approximately. The capacity of the blocking condenser was 15 n'iifcromicrofarads, the capacity between the grid and plate of the tube was about 5 mieromicrofarads, while the capacity of the lixed condenser in the auxiliary circuit was also about 5 micromicrofarads. The system oscillated very steadily at a wave length of approximately two meters, and the power radiated was substantially 3() watts with 2200 volts applied to the plate of the tube.

At such high frequency, it is highly probable that neit-her the circuit comprising the tube elements nor the auxiliary circuit com-v prising the single-turn inductor and the fixed condenser oscillates as does the ordinary and well known tuned-circuit. I have not definitelyl established the exact mode in which oscillations take place, though it appears highly probable that phenomena are present analogous to those manifested when stationary waves are caused to exist on Leeherwires. At any rate, the conductors leading 'Iel to the plate -aud 'filament have potential loops developedbn't'hem near .theA points Where they extend througlrthe opposite ends of the thermionie device.' y i -It is' customaryto intel-pose radio-frequency choke coils between the `various sources f supply and the tubeV elements, in order that energy at'adio frequency, shall not be by-passed through the said sources. Such choke-coils, of "necessity, consume an appreciable amount offenergy, and consequently lower the eiiiciency of a system designed to generate oscillations at ultra-high frequencies. I have, accordingly, replaced the aforesaid radio-frequency c oke coils by plain conductors, each of which is one uarter of a wave-length long. I have furtier fixed the potential of the points at Whicht-hese conductors are attached to the voltage sources by grounding the said points through condensers having large capacity. The conditions precedent to the establishing of standing Waves on these conductors are, therefore, present. The ends thereof nearest the tubes are at what might be termed voltage loops, and the opposite ends are equivalent to voltage nodes. When in operation, therefore, no energy at radio frequency is transferred from either the filament or the plate to the voltage sources associated therewith` and the eliieiency of the system is materially increased. It is largely to the use of such quarter wave-length leads that I attribute my success in being able to cause the radiation of an amount of power at ultrahigh frequencies much' greater than is possible with systems known to the prior art.

The auxiliary circuit 18' may be dispensed with in the event that it is not desirable to radiate any large amount of power. A thermionic device may be substituted for the spark gap in the Well known Hertz oscillator, in which case, the said device forms' apart of the radiating structure, per se. A system so arranged is illustrated in Fig. 2.

Referring specifically to Fig. 2, a therniionic device 50, having a filament 51, a grid 52 and a plate 53, is supplied with plate-potential from a source 54 through a quarter-wave-length conductor 55 and With filament power from a source 56 through quarter-Wave-length conductors 57 and 58. A C-battcry 60, connected in series with a resistor 61. iixes the potential of the grid with respect to the filament. or the C-battery may, if desirable. be omitted. I have not shown the grid-leak resistor 61 as being interposed in a quarter-Wavelength conductor. inasmuch as, in an actual physical embodiment of this modification of my invention, the grid and filament=leadin Wires would be quite close together.

A plurality of fixed condensers 62, 63, 64 and 65 of large capacity are interposed between the poles of the ptentialsolurces 54,

56, 60 and gi'on'h and,v "tlileefore,'ffix the. potential of the" lower :ends ofthel 'quarter Wave-length conductors 5 ,"'57"and'58.` f A straight comluctor 66"'is'aixcd to the lead extending fromthe plate'ofthe ther-j mionic device, and asimilar conductor 67 is aflixed tothe grid-le'ad. There is a definite amount of distributed v'capacity'between these extensions of the plateandf'giid" conductors which is represented by a condenser 68 shown'- in dotted lines. Y

The system illustrated in Fig. 2,' when en-4 ergized, tends to Voscillate atafrequenc'y determined by the over-all distance Vbetween the ends of the conductors 66 and 67, the" stray capacity existing between them, andthe capacity etweentlie grid and the plate of the tube, unless the latter is'very large.v This frequency will be found to` correspond, in general, to a Wave length which is equal" to the said over-all distance, the equivalence being modified by the inter-electrode capacity. Such a condition follows from the factthatl the free ends of the conductors-66 and 67 are, of necessity, potential loops-and from t-he` fact that'a potent-ialloop exists: on thcV grid and plate. fTh-epres'ence of these three potential loops indicates tha't-fthe-Yshortest wave which can'be generated is one having a wave length corresponding to the said over-f all distance. A

The system illustrated in ll`ig."2, is'perhaps, a more eiiicient radiator thanfthe system shown in Fig. l; vIt sprinoipallyof value in connection With:=potable transmitl ters designed to cover short'l distances, since it obviates the necessity for supplying Qanl additional radiating structure of any description. r A system `constructed according to my invention, as illustrated in Fig. l, is principally advantageous in that it4 permits a'larger proportion ofthe power input-to'be effectively radiated inthe form ofuit-ra-:high frequency oscillations than-analogous sys-l tems known to the prior art.. The"oscilla-; tions produced are remarkably Asteady 'in' amplitude and" the frequency variation has been found to be much sl'naller-than When4 the stabilizing 'circuit is`7notused--s In this@x latter respect, luyimprovedsystem is inucl'r superior to anything'ivith which I have heretofore been acquainted.

Although I have shownand-desrib'cd only' a few specific embodiments of my invention, many modifications and adaptations thereof 'will be apparent-'to thoseskilled in theart.

My invention, therefore, isnot to be limited except insofar as is necessitated bythe prior art and by the spirit of the 'appended claims.

I claim as my invention: Y v

1. Electrical ,apparatuslinclu'ding a-thermionic tube connected bysuitablecircuit net-y works to sources *of potential and arrangedv to generate high-frequency oscillations of ai leo ris

definite wave-length, characterized in that the length of the connection between at least one of the elements of said tube and one of said sources is substantially one-quarter of said wave-length.

2. Electrical apparatus including a therinionic tube connected by suitable circuit networks to sources of potential and arranged to generate high-frequency oscillations of a definite wave length, characterized in that the length of the connections between a plurality of the elements of said tube and said sources are each substantially one-quarter of said wave-length.

3. In an oscillation generator arranged to generate oscillations of a definite wave length, a therinionic device comprising an anode, a source of potential for said anode, and a connection between said source and said anode of a length substantially equal to one-quarter of the wave-length of the oscillations generated.

4. In an oscillation generator arranged to generate oscillations of a definite wave length, a thermionic device comprising a cathode, a source of potential for energizing said cathode, and connections between said source and said cathode of a length substantially equal to one quarter of the wave-length of the oscillations generated.

5. In an oscillation generator, a thermionic device having a plurality of electrodes, an oscillating circuit having a frequency determined by the capacity between certain of said electrodes and materially iniuenced by the length of the leads extending from said electrodes to the exterior of said thermionic device, a second stabilizing circuit comprising an inductor and a condenser of the order of the inter-electrode capacity, and connections between said second circuit and certain of the said electrodes.

6. In an oscillation generating system, a thermionic device having a cathode, an anode, and a cont-rol electrode, an oscillatory circuit including a stopping condenser and the inter-electrode capacity between said anode and said control electrode, the period of said circuit being determined by the said inter-electrode capacity and by the length of the connections whereby said stopping condenser is included in circuit, and a stabilizing circuit coupled to said oscillatory circuit, said stabilizing circ-uit including a condenser of the order of magnitude of said iliter-electrode capacity and having a period substantially equal to thc-period of said'oscillatory circuit..

Iii-testimony whereof, I have hereunto subscribed my name this 30th day of June, 1927.

PHILLIPS THOMAS. 

